To　obtain　a　stabilizer　for　an　underactuated　surface　vessel　with　disturbances,　an　L2-gain　design　is　proposed.　Surge,　sway,　and　yaw　motions　are　considered　in　the　dynamics　of　a　surface　ship.　To　ob-tain　a　robust　adaptive　controller,　a　diffeomorphism　transformation　and　the　Lyapunov　function　are　employed　in　controller　design.　Two　auxiliary　controllers　are　introduced　for　an　equivalent　sys-tem　after　the　diffeomorphism　transformation.　Different　from　the　commonly　used　disturbance　ob-server-based　approach,　the　L2-gain　design　is　used　to　suppress　random　uncertain　disturbances　in　ship　dynamics.　To　evaluate　the　controller　performance　in　suppressing　disturbances,　two　error　sig-nals　are　defined　in　which　the　variables　to　be　stabilized　are　incorporated.　Both　time-invariant　dis-continuous　and　continuous　feedback　laws　are　proposed　to　obtain　the　control　system.　Stability　analysis　and　simulation　results　demonstrate　the　validity　of　the　controllers　proposed.　A　comparison　with　a　sliding　mode　controller　is　performed,　and　the　results　prove　the　advantage　of　the　proposed　controller　in　terms　of　faster　convergence　rate　and　chattering　avoidance.